Swell dance circle working (7)
I believe the answer is:
balloon
'swell' is the definition.
(both can mean to expand or increase)
'dance circle working' is the wordplay.
'dance' becomes 'ball' (ball is a kind of dance).
'circle' becomes 'O' (O is a circle).
'working' becomes 'on' (on can mean working or activated).
'ball'+'o'+'on'='BALLOON'
(Other definitions for balloon that I've seen before include "Air-filled bag" , "Brandy glass" , "Inflate" , "Swell, increase rapidly" , "plaything" .)